Melanoma is a malignant tumor produced by the pigment-producing cells of the skin termed melanocytes. Melanoma is the most deadly skin cancer, accounting for only about 4% of all cases but 79% of skin cancer deaths. Melanoma of the skin accounts for 160,000 new cases worldwide each year, and is more frequent in white men. Melanoma occurs most often in the skin but may also develop in the eye or in the lining of the nose, mouth, or genitals. Subsequently, melanoma can spread to internal organs.
Despite many years of intensive laboratory and clinical research, the sole effective cure is surgical resection of the primary tumor before it achieves a thickness of greater than 1 mm. There are no current therapies that have a statistically significant survival benefit in advanced melanoma. Lactate dehydrogenase (LDH) tests are often used to screen for metastases, although many patients with metastases (even end-stage) have a normal LDH; extraordinarily high LDH often indicates metastatic spread of the disease to the liver. It is common for patients diagnosed with melanoma to have chest X-rays and an LDH test, and in some cases CT, MRI, PET and/or PET/CT scans. Although controversial, sentinel lymph node biopsies and examination of the lymph nodes are also performed in patients to assess spread to the lymph nodes.
Diagnosis of melanoma often poses challenge. Sometimes the skin lesion may bleed, itch, or ulcerate, although this represents generally a late sign. In some cases, melanomas may “regress” or spontaneously become smaller or invisible; however, the malignancy persists. Amelanotic (colorless or flesh-colored) melanomas do not have pigment and may not even be visible. Lentigo maligna, a superficial melanoma confined to the topmost layers of the skin (found primarily in older patients) is often described as a “stain” on the skin. Some patients with metastatic melanoma do not have an obvious detectable primary tumor.
When there is distant metastasis, melanoma is generally considered incurable. The five year survival rate is less than 10%, where the median survival is 6 to 12 months. Metastases to skin and lungs have a better prognosis, whereas metastases to brain, bone and liver are associated with a poor prognosis.
There is not enough definitive evidence to adequately stage, and thus give a prognosis for ocular melanoma or mucosal melanoma (e.g. rectal melanoma), although these tend to metastasize frequently. When a melanoma has regressed, it is impossible to know its original size and thus the original tumor is often worse than a pathology report might indicate. Therefore, more sensitive, and effective means of identifying and treating melanoma would be of much interest.